SEATTLE -- An immigration rights march that drew thousands of people of all ages and races was marred by a car that struck a group of marchers at a downtown intersection.

Demonstrators surrounded and began beating on the car after it hit and slightly injured three people Monday afternoon, and the driver was arrested for investigation of assault, police Officer Debra Brown said.

Five other people were arrested for possible weapons violations and one person for obstructing police, Brown said.

Police would not give an official estimate of Monday's crowd, while estimates by organizers ran from 30,000 to 65,000.